1. Field of the Invention
The present invention is related to a lighting system and in particular, to a control method of a lighting system,
2. Description of the Related Art
Recently, with a great amount of light-emitting diodes (LEDs) being adopted in lighting systems, more and more LED lighting systems are employing AC power as the power source thereof. Traditionally, when an AC power source for a plurality of LED lighting systems is used, the AC power will be full-wave rectified via a bridge rectifier, and then a rectified voltage will be outputted to the plurality of LED lighting systems.
In order to improve power conversion efficiency, the LED circuits using AC power are turned on gradationally, so that different numbers of LEDs can be turned on by the different input voltages, and the current flowing through the LEDs can be controlled. Different number of LEDs are usually turned on or off by switches; however, instantaneous switching may cause an instantaneous change of current, and may increase the third harmonic (THD) of the current. Also, the instantaneous change of current also induces electromagnetic interference (EMI).